A367004 a(n) is the smallest prime factor of n*2^n+1.

3, 3, 5, 5, 7, 5, 3, 3, 11, 7, 13, 13, 3, 3, 17, 17, 5, 11, 3, 3, 23, 13, 5, 5, 3, 3, 7, 29, 31, 17, 3, 3, 47, 19, 37, 37, 3, 3, 41, 41, 13, 23, 3, 3, 11, 5, 7, 7, 3, 3, 53, 7, 5591, 29, 3, 3, 5, 31, 37, 61, 3, 3, 5, 5, 67, 5, 3, 3, 7, 37, 11, 41, 3, 3, 149

Offset: 1

Author

Sean A. Irvine, Oct 31 2023

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..914 (terms 1..350 from Robert Israel)

Crossrefs

Cf. A002064, A005849, A020639, A049479, A367002, A367003, A367005.

Programs

Maple

seq(min(numtheory:-factorset(n*2^n+1)), n=1..100); # Robert Israel, Nov 09 2023

Mathematica

Table[FactorInteger[n 2^n+1][[1,1]],{n,80}] (* Harvey P. Dale, Aug 14 2024 *)

Formula

a(n) = A020639(A002064(n)).